If the Pokémon holding a Focus Band is hit by a damagingmove that would cause it to faint, there is a ~12% (30/256) chance the Focus Band will activate and cause its holder to survive with 1 HP. If Focus Band activates on any strike of a multistrike move, the holder will survive every subsequent strike of the attack. Focus Band can allow the holder to survive Future Sight. It cannot activate as a result of self-inflicted confusion damage.
Generations III and IV
The Focus Band now has a 10% chance to activate. Focus Band now allows its holder to endure self-inflicted confusion damage.
Focus Band can allow the holder to survive Doom Desire.
Generations V onward
If Focus Band activates on a multistrike move, the holder will now only survive the strike that activated it, and the Focus Band will have to activate independently on each subsequent hit.
In Pokémon UNITE, the Focus Band is a held item that recovers user's HP for 3s when below 25%; specifically by 8/11/14% of missing HP with 100/90/80s cooldown at Grade 1, 10, and 20 respectively. It also increases the user's Defense and Sp. Defense: by 2 and 0 respectively at Grade 1 and by 30 each at Grade 30.